Gas turbine engines are used extensively in commercial aerospace industries as they provide efficient propulsion machinery for propelling airplanes and other aircraft. As the gas turbine operates at different operational cycles, for example during take-off, in-flight maneuvering, and deceleration for landing, the thrust curve will fluctuate based upon, in part, the performance and environmental demands that are placed on the aircraft. Engine health monitoring and calculating current thrust loads on the aircraft therefor are important for many reasons, not the least of which so as to aid in the understanding of current operating conditions as well as to provide predictability of future performance demand requirements.
There are many other reasons why it is desirable to be able to estimate thrust from an engine. Thrust estimation can be used to measure the mechanical conditions for example a damaged propeller, damage fan or degraded engine. When the engine controller looks only to throttle settings, safety is obviously a concern. It is easy to measure thrust of an engine running on a test bed however; it has been proved difficult to measure thrust of an engine installed in a vehicle. The current proposal helps address this concern.
Systems for estimating thrust that use measured parameters such as pressure and temperature at various points in the engine and the speed of rotation of each of the spools in the engine are very complex and are still not very accurate because of large random variations in these parameters which occur within the engine. These variations make it very difficult to relate the simultaneous values of different parameters or the same parameter at two different points in an engine in order to calculate the thrust being produced by an engine, and as a result the derivation of thrust is complex and unreliable.
Notwithstanding, the thrust from an engine in one method is estimated by complex engine models using several parameters, including measurements of temperature and pressure. However, as discussed herein, temperature does not result in thrust and pressure does not necessarily result in thrust either. These complex models require expensive and delicate computers and often the onboard controller is not capable of running such models. As a result the models are simplified to be approximately related to a few parameters or maybe the ratio of a few parameters or even just a single parameter to estimate thrust. Some control systems reduce thrust to a simple functional shaft speed, or pressure ratios in the engine or pressure ratios weighted by temperatures. When a pilot or autopilot pushes the power level forward, the system looks for more of that single parameter. The result is that thrust is not well quantified and may require different throttle settings to achieve the same thrust on different days.
Another concern is the autopilot maybe not be well tuned for certain flight conditions and would result in the autopilot searching for a throttle setting, constantly increasing and decreasing the throttle, as the engine controller overestimates the amount of fuel required to provide certain additional thrust. There are of course additional considerations.
By not allowing for accurate estimations during transient conditions, an algorithm could incorrectly perceive the increase or decrease in thrust during a bank turn or when the aircraft experiences a head wind. In these situations the control system might be incorrectly adjusted during transient conditions, for example a bank. If an engine health monitoring system were used with such a system it could inaccurately flag an engine as needing repair. Therefore, it would be desirable to provide a method and system for estimating thrust during steady-state and transient conditions.